Abstract
"This thesis reports the potential of commercial silica based fibres with different Ge doped core
concentrations for radiation dosimetry. Fibre samples studied included multi-mode 4 and 6%Ge
doped core purchased from CorActive, Canada, single-mode 17%Ge 1%B (GeB) and undoped
coreless silica fi bres supported by Fibercore, UK. Scanning Electron Microscope (SEM) and Energy
Dispersive x-ray Spectroscopy (EDS) measured the effective atomic number of these fi bres
between 14 and 18 which is similar to human bone, the chemical composition was con firmed to
be uniform across the fi bre cross-section. In a fi ve millimeter fi bre length thermoluminescence
study, the undoped silica fi bre had no thermoluminescence (TL) response. The 6% Ge doped fibre
showed the best sensitivity with and without core size correction, 15082±687 counts•mm-1•Gy-1
and 7.69±0.35 counts•mm-1•Gy-1•µm-2 respectively. This fi bre also represented an optimal
concentration; over this amount dopant contributed to the self-absorption of luminescence.
The TL glow curve from Ge doped fibre exhibited a broad peak shape extending beyond
400 °C. When increasing Ge dopant from 4 up to 17 %, the main peak temperature, TM was shifted
to lower temperature; from 317±2 to 249±3 °C. This result suggests that different dosimetry
readout temperature settings should be applied for different percentage doped Ge fibre. This fi nding
also bene fits new TL material development, with the advantage of lower readout temperature.
TolAnal CGCD software and peak fi tting function in MATLAB revealed that overlapping of fi ve
sub-peaks caused the broad peak shape. This software was also consistent with the Chen peak
shape method in that the electron trap energies ranged from 0.5 to 1.5 eV. This helps consider
the sufficient activation energy to create recombination leading to luminescence. For medical
applications the results indicate using a 6%Ge fibre readout at 302 °C.
OpticalStudio (Zemax) ray tracing software was applied to study TL propagation in 4%
Ge doped fi bre. Where the luminescence originates in core volume, 68±5% of luminescence is
emitted around the fi bre side. This supports that TL readout from fi ve millimeter fi bre dosimeter,
by facing the long dimension of the fi bre towards the photomultiplier (PMT), can maximise the
collected TL signal. The 27±5% of luminescence exited from the combined fibre ends provides an
opportunity to measure signal from fibre ends when the long length fi bre (metres) is used. In
Optically Stimulated Luminescence (OSL) investigation, two metres of 4 and 6%Ge doped fibres
were tested with two laser wavelengths; 1540 and 532 nm. As high attenuation induced by radiation
took place on the whole fibre length, the laser intensity was reduced, contributing to the absence
of the OSL signal. The TL glow curve study after laser treatment exhibited that the energy from
532 eV is sufficient to release trapped electrons."